The conventional image-reading devices divide the reading area for each reading unit into a plurality of sub-regions, and the reading units output data read from the original by sub-region. The read data outputted for each sub-region is in the form of an analog signal. An analog front end (AFE) with an A/D converter circuit is provided for converting the analog signals outputted from the reading units to digital read signals. The AFE has a plurality of channels and, hence, can simultaneously process read data for a number of sub-regions equivalent to the number of channels.